Apart from the advantage that they possess high resolution, maskless particle projection systems (e-beam or ion beam writers) have the disadvantage of low productivity at the structural level of today, which is a result of the serial writing process of the particle beam. Because of this, renewed efforts are being made to increase the overall productivity of a particle projection system by employing a greater number of particle beams in parallel. One very promising approach consists in using a controllable aperture plate to deflect a multiplicity (up to several million) of partial beams that are together projected on the substrate.
U.S. Pat. No. 6,403,973 discloses a method for electron beam exposure and a device suitable for using this method. A substrate to be exposed is placed on a continuously moving table. In the process, the position of the table and the required beam position are determined and any deviations are corrected, making possible a highly precise, glitch-free adjustment of the individual exposure positions on the substrate. However, this device operates using a single electron beam. An aperture plate is not provided to generate a multiplicity of partial beams from the individual electron beams. Furthermore, exposure is not continuous, but rather takes place as a sequence of individual shots.
U.S. Pat. No. 4,853,870 also discloses an electron beam exposure system that takes into account the position of the table during exposure and corrects any potential deviation via a two-step excursion of the electron beam. Here, too, only a single electron beam is used for exposure by keying and reading the beam by means of a sequence of shots.
U.S. Pat. No. 4,477,729 describes an electron beam exposure system that works by using a continuous writing system. Here, the structures to the generated are exposed as a sequence of adjacently lying partial structures, whereby the set position of the table is given by a corresponding sequence of closely adjacent reference positions of the partial structures. In this system, too, corresponding correction is carried out between the current table position and the current writing position of the electron beam. The forward transfer of a partial field of action to the next, however, presupposes a blanking of the particle beam. In addition, this system uses only a single particle beam.
A further exposure arrangement and method using a single electron beam is disclosed in U.S. Pat. No. 4,147,937. The described arrangement also works by tracking the beam-to-table position on the basis of a positional measurement system. However, exposure is done by controlling specified set positions in a step-and-go mode.
U.S. Pat. No. 4,153,843 discloses an exposure system with several beams. Here, a two-dimensional array with several openings is provided in the beam path of an electron beam exposure system. The surface of the array is illuminated by the electron beam and imaged in miniature on a substrate. Individual beams can be switched off by means of the aperture plate so that these do not reach the substrate. The aperture plate thus ensures that the dosage of electrons on the substrate can be regulated at each addressed position of the electron beam so that the proximity effect can be corrected. Correction of table deviation and corresponding control of the electron beam are not disclosed.
U.S. Pat. No. 5,144,142 discloses a particle beam system that comprises an aperture plate to produce the corresponding partial beams. The aperture plate array comprises n lines and m columns of openings that are arranged in a two-dimensional fashion on a substrate. A pair of deflection electrodes is arranged at each of the openings. Furthermore, n- and m-bit-long shift registers are provided on the substrate in order to direct the deflecting voltage corresponding to the pattern data to the m pairs of electrodes of each line. Exposure occurs by shifting the pattern data through the aperture array while simultaneously deflecting the beam bundle. Here, the current table position determined by a laser interferometer is compared with the set data position, and the difference is taken into account during deflection. A device for synchronizing the table system with the shifts in the aperture plate is, however, not disclosed.
U.S. patent application US 2003/0155534 A1 discloses a maskless exposure system for particle beams. A multi beam is formed by means of a stack of aperture plates, whereby a blanking plate with an integrated shift register and storage circuitry enables level adjustment of each partial beam in synchrony with the scanning movement of the table system. In order to fix the pixel images during exposure on the moving substrate, a deflection system controlled by sawtooth voltage is proposed. A technical solution for synchronizing table movement with the shifts in the blanking plate and the deflection movement of the multi particle beam is, however, not disclosed.
The article “Programmable Aperture Plate for Maskless High-Throughput Nanolithography” by Berry et al.; J. Vac. Sci. Technol. B 15(6), November/December 1997; pp. 2382-2386, discloses a programmable aperture array that comprises 3000×3000 apertures that can be electronically individually adjusted and therefore switched on and off in order to achieve dynamic control of beam throughput. The pattern to be exposed is loaded successively from one side into the aperture array and pushed through to the other side by means of integrated shift steps. The wafer to be written on is moved in synchrony to it. Control or correction of the current table position is not disclosed in this article.
All known publications that treat beam tracking on the basis of a laser path measurement system to determine table position proceed from the principle of a fixed writing field. Beam tracking compensates for the deviation in the current table position from a specified set position that is indicated by the laser path measurement system and fixes the midpoint of the current writing field. Because the maximum size of the writing field is limited as a result of imaging errors of the particle optic, the surface of the substrate is exposed by arraying a multiplicity of writing fields (with overlaps under certain circumstances). A blanking of the total beam is required for repositioning the writing fields; uninterrupted writing of a strip across the entire substrate is therefore not possible.
The documents that mention aperture plate arrays either do not go further into the problem of beam-to-table positioning, or they provide for beam tracking that is independent of pixel shifting in the aperture array. In the latter case, the aperture array can only be used to scan across the breadth of a fixed writing field, as just mentioned. Otherwise, systematic position errors occur as a result of a lack of synchronization between the table system and the aperture plate system.
Straying of a shift phase from the current position values of the moving table system, i.e., upon reaching the subsequent set position, in which the aperture array is advanced by one phase does not represent a solution to the problem because intolerable time—and therefore dosage—fluctuations occur as a result of the imprecise table travel.